O'Brien begins to answer this by claiming that the Party could really care less about the petty crimes people commit, in fact,

The Party is not interested in the overt act: the thought is all we care about. We do not merely destroy our enemies, we change them.

This ability to change people is much different than control movements of the past. O'Brien notes the flaws of great movements of religion and politics in The Spanish Inquisition, the Russian Communists, and the German Nazis. According to O'Brien, all of these groups contained some of the same flaws: they could destroy peoples and they could degrade them, but they could not change them. This is not power. Power occurs when change happens. The Party seeks total power because in each of these historical cases

after only a few years the same thing had happened over again. The dead men had become martyrs and their degradation was forgotten. Once again, why was it? In the first place, because the confessions that they had made were obviously extorted and untrue. We do not make mistakes of that kind. All the confessions that are uttered here are true. We make them true.

In all of history, new generations remembered the past. They acted on the ills they saw forefathers experience. O'Brien's Party creates new truth so that new generations cannot remember the past.

O'Brien gives even more reason:

That the Party did not seek power for its own ends, but only for the good of the majority. That it sought power because men in the mass were frail cowardly creatures who could not endure liberty or face the truth, and must be ruled over and systematically deceived by others who were stronger than themselves... That the party was the eternal guardian of the weak, a dedicated sect doing evil that good might come, sacrificing its own happiness to that of others.

Ironically, O'Brien seems to believe it all. However, after some time apart, and further questioning from Winston, O'Brien finally admits:

The Party seeks power entirely for its own sake. We are not interested in the good of others; we are interested solely in power. Not wealth or luxury or long life or happiness: only power, pure power. What pure power means you will understand presently. We are different from all the oligarchies of the past, in that we know what we are doing.

POWER MEANS CONTROL. The Party is interested in complete control and dominion of mankind.